[v3] Extract Concepts from v2 exercise: secret-handshake

[rajeshpg]

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Extract the list of concepts required to solve the v2 <LANG> exercise: secret-handshake. For each concept, describe why it is required to solve the exercise. Keep in mind that an exercise can have multiple approaches (you can find community solutions here: https://exercism.io/tracks/scala/exercises/secret-handshake/solutions). The goal of this task is to help determine the total list of concepts that make up secret-handshake.

The list of concepts should be stored in the following document: languages/secret-handshake/reference/exercise-concepts/secret-handshake.md. Use this link to create a PR to add this document.